While the global HIV/AIDS epidemic has disproportionately burdened socially and economically marginalized populations in sub-Saharan Africa, HIV treatment scale-up has dramatically improved access to antiretroviral therapy (ART) for all. Nonetheless, for ART to decrease morbidity and mortality, sustained treatment adherence is essential. When ART is provided free of charge, the greatest barriers to treatment adherence for marginalized populations remain structural: cost of transportation to clinic, food insecurity, homelessness, and opportunity costs. Such structural factors lead to treatment interruptions for migrants even more than for their stationary counterparts because migrants' mobility and irregular employment make income, transportation, food, housing, and proximity to health care even more uncertain. Thus, migrants are at very high risk for ART treatment interruptions. The public health ramifications of treatment interruptions in migrant populations are substantial because migrants may contribute significantly to the spread of HIV and antiretroviral drug resistance because of the combination of interruptions and migration. Though a large body of literature explores structural barriers to ART treatment adherence, few studies have focused on treatment interruptions specifically in labor migrant populations. My long-term career goal is to become an independent physician-investigator who brings together clinical medicine, anthropology, and public health to understand and address the structural (social, economic, and political) complexities of the HIV epidemic in sub-Saharan Africa. As an MD-PhD candidate in anthropology, I need additional mentorship and training in public health to help me craft an interdisciplinary research approach. My three-year Training Plan will include coursework, supervised field research and data analysis, manuscript writing, and attendance and presentations at professional meetings. I will utilize this training and my Project Co-Sponsors' expertise on conducting ART adherence-related research in sub-Saharan Africa to accomplish my scientific objective: to acquire a more robust understanding of reasons for ART treatment interruptions specific to HIV-infected labor migrants in South Africa. In pursuit of this objective, I will seek to achieve two specific aims: (1) characterize reasons for ART treatment interruptions among HIV-infected labor migrants in South Africa using qualitative research methods and (2) develop a conceptual model for how structural factors lead to treatment interruptions in this migrant population. South Africa is an ideal setting for this research becaus it has more HIV-infected citizens than any other country, and many of its citizens are either labor migrants or family/household-members of labor migrants. The proposed research is innovative because it targets an understudied population both at high risk for ART treatment interruptions and integral to the spread of HIV. It is significant because it has the potential to inform future interventions and health policies by providing a more comprehensive understanding of the structural factors driving ART treatment interruptions among labor migrants.